Resonance fluorescence 492 Subject

Sensitized fluorescence, especially when emitted in the decay of resonance states, has properties similar to those of resonance fluorescence, being equally subject to imprisonment and being sensitive to the presence of polarization and of ambient magnetic fields. It must thus be studied under conditions as well controlled as those necessary for studies of resonance fluorescence. 

Diatomic cations, neutral molecules, and anions represent the type of inorganic species which has been most extensively studied by resonance Raman spectroscopy. Iodine in the gaseous, dissolved, and matrix-isolated states has been the subject of particularly detailed studies, and it is this molecule for which the greatest number of members (25) of a resonance Raman progression has so far been observed (66). The relation between resonance Raman and resonance fluorescence spectra has been discussed in Section 2, but it is worth illustrating the general principles involved by reference to the work on iodine. 

Scattering Phenomena.—A review has appeared of the scattering of depolarized light by simple fluids.437 Pre-resonance Raman spectra of NH3, CH8NH2, form-amide, cw-dichloroethylene, propargyl alcohol, and pyrazine 438 resonance Raman scatter of I2 in solution and in inert matrices 439 time-resolved resonance fluorescence and resonance Raman 440 and stimulated resonance Raman scattering 441 pseudo-Raman spectra in stacked benzene molecules 442 and birefringence in CS2 443 have been the subjects of recent reports. 

The powerful technique of two-photon absorption, which permits limitations of Doppler broadening to be overcome (see Chapter 1), has been used in a study on sodium atoms in which the Stark effect in the 5s 2Si and 4d D and D levels was observed.188 The radiative lifetimes of the S and D Rydberg levels of Na,189 the use of laser-induced resonance fluorescence for the measurement of small concentrations of Na vapour,170 the quenching of Na(32P) and K(42P) by N2, 02, H2, and HaO,171 the chemi-ionization reactions of photoexcited atoms,172 and excitation of the K(42P ) level in collisions with rare-gas atoms173 have been the subjects of recent reports. 

From the beginning of this century experiments using resonance radiation and resonance fluorescence have been largely responsible for our increasing understanding of excited atoms and their interaction with radiation. In the 1920 s the polarization of resonance fluorescence from atoms subjected to external magnetic fields was studied in detail by Hanle and used to measure radiative atomic lifetimes. 

Introduction and experimental techniques. In previous sections we drew attention to the fact that, in both the classical and quantum theories, expressions derived for the intensity of resonance fluorescence from atoms subjected to an external magnetic field, equations (15,3) and (15.23) respectively, contain terms which may lead to a modulation of the intensity at the Larmor frequency or its second harmonic. This radio-frequency modulation has been observed in several different kinds of experiment, the simplest of which makes use of pulsed excitation and time-resolved detection of the fluorescent light. 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

Fig. 12.14. Resonance Raman imaging results for the macular pigment distribution in the retina of a volunteer subject, a Typical gray-scale image obtained after subtraction of fluorescence background from pixel intensity map containing Raman response and superimposed fluorescence background, b Gray-scaled, three-dimensional representation of gray-scale image...

Fig. 12.16. Resonance Raman images of macular pigment distributions obtained for the same subject with the Raman method (a) and with a fluorescence-based imaging method (b) (c) comparison of integrated pigment densities obtained for 16 volunteer subjects with both imaging methods. A high correlation coefficient of R=0.89 is obtained for the correlation between both methods...

The elucidation of the structure, dynamics and self assembly of biopolymers has been the subject of many experimental, theoretical and computational studies over the last several decades. [1, 2] More recently, powerful singlemolecule (SM) techniques have emerged which make it possible to explore those questions with an unprecedented level of detail. [3-55] SM fluorescence resonance energy transfer (FRET), [56-60] in particular, has been established as a unique probe of conformational structure and dynamics. [26-55] In those SM-FRET experiments, one measures the efficiency of energy transfer between a donor dye molecule and an acceptor dye molecule, which label specific sites of a macromolecule. The rate constant for FRET from donor to acceptor is assumed to be given by the Forster theory, namely [59,61-64]... 

PBO was found to be unstable when subjected to add hydrolysis- When JUC -PBO was refluxed with 1 mol L HCl for 1 hour, a single fluorescent radioactive compound was formed. This compound was isolated by preparative high-performance liquid chromatography (IIPLC) and identified by gas chromatography-mass spectroscopy (GC-MS), high-resolution MS, nuclear magnetic resonance (NMR), and comparison of HPLC retention time with a synthetic standard. 

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